Shrink fit fabrication method for fluid injectors

ABSTRACT

A method for fabricating a fluid injector having a circular boss containing fluid exit passageways extending from a main body, comprising providing an annular peripheral groove on the boss, shrink-fitting a ring by thermal steps on the boss peripheral surface outwardly from the annular groove and bridging the groove, thus forming a fluidtight manifold therewith in communication with the exit passageways.

United States Patent 1 1 3,591,907

[72} inventor James L. MacMunn [56] References Cited s: Park, Calif-UNITED STATES PATENTS P 1,692,966 1 1/1928 Treiber 29/l56.7 med P':'.2,245,608- 6 1941 Rodgers 18/12 4 3,137,445 6/1964 Hirschfeld 6! al239/431 x Pat. No. 3,508,712 [45] patented 1'"! 13 1971 PrimaryExaminer-John F. Campbell [73] Assignee North American RockwellCorporation Amman Emmmer-D' Re'ley Attorney-William R. Lane [54] SHRINKFIT FABRICATION METHOD FOR FLUID INJECTORS 2 Chin 2 Drawing a ABSTRACT:A method for fabncaung a fluid in ector havmg a circular boss containingfluid exit passageways extending [52] US. Cl 29/157 C, from a main body,comprising providing an annular peripheral 2 2 l 2 1. 2 groove on theboss, shrink-fitting a ring by thermal steps on [5 1] Int. CL 823p 15/26the-boss peripheral surface outwardly from the annular groove [50] Field0| Search 239/431, and bridging the groove, thus forming a fluidtightmanifold 534; 29/ [57, 447 therewith in communication with the exitpassageways.

PATENTED JUL 1 31911 A T TORNE Y SHRINK FIT FABRICATION METHOD FOR FLUIDINJECTORS This application is a division of application Ser. No.584,214, filed Oct. 4, 1966, now US. Pat. No. 3,508,712.

This invention relates to a fuel injector and more specifically to itsunique structure and a technique for assembling the injector from twocomponents.

The various types of fuel and oxidizer injectors presently being used inthe rocket engine art, particularly, are becoming increasingly expensivein terms of cost and time required for assembly. Assembling proceduresare complicated due to the numerous components which must be preciselyconnected together according to rigid standards. Conventional injectorshave their components secured together by welding or brazing techniques,or with expensive high-strength connecting elements. As the number ofrequired connecting elements or weld joints is increased there is acorresponding increase in the risk that one or more is defective. Thetime consumed by the necessary quality control certification isexcessive.

When connecting elements are employed, potential leakage paths alwaysexist. Pressure surges occurring in injectors at unpredictable timesoperate to rupture joints formed by welding or brazing. As a result, aninjector ring or other component can be blown off causing disasterousresults. These components that are prone to being blown off, due tomachining difficulties, are customarily assembled on the backface(opposite the injector face) so that harmful effects are caused outsideof the combustion chamber. In such a case, the vehicle itself or thedevice incorporating the injector can become severely damaged ordemolished. In addition, once components in conventional injectors areblown off" or otherwise ruptured, the condition is irreparable.

The foregoing disadvantages of conventional injectors are avoided by theinstant invention which can be used to quickly and inexpensivelyassemble an injector having only two components. Neither welding norbrazing techniques not connecting elements of any kind are used inassembling the injector, thus minimizing costs as well as risk ofdefects.

Briefly described, the instant invention comprehends a unique injectorhaving only two components which are assembled by a shrink-fittingtechnique. The two components are a main body integrally formed with amanifolded circularshaped or boss portion extending therefrom and aring. When the two components are at ambient or the same temperature,the inner diameter of the ring is smaller than the outer diameter of theboss portion. Prior to assembling the components, the ring is heateduntil its inner diameter expands to exceed the outer diameter of theboss portion, at which time the ring is positioned onto the bossportion. The ring is then shrunk by cooling causing the two componentsto become tightly sealed together. In order to eliminate excessiveweight and still provide the necessary sealing surface between the twocomponents, a circular recess is formed in the main body to receive oneend of the ring.

An object of this invention is to provide an injector and a techniquefor assembling a two-component injector requiring no welds or connectingelements.

Other objects and advantages of the instant invention will be clearlyunderstood when the following detailed description is studied inconjunction with the detailed drawings in which:

FIG. 1 is a cross-sectional side view of the injector with the main bodyand manifold ring components completely assembled.

FIG. 2 is an enlarged cross-sectional view of that portion of the mainbody encircled by line 2 as shown in FIG. 1.

An embodiment of a fuel injector assembled according to the instantinvention is shown in FIG. 1. An injector assembly 10 is depicted whichis to be used for supplying fuel to a thrust chamber assembly 13 (shownin part only). Injector I may be used with any suitable type of heatengine such as a diesel engine or a rocket motor or the like. Forpurposes of clarification, the assembling and construction of injectorassembly 10 will be explained in terms of its use with a rocket motor(not shown). A circular disc-shaped main body 12 is formed with a raisedcircular-shaped boss 14 which, when injector assembly 10 is actuallybeing used, extends forwardly so as to project slightly into the rocketmotor combustion chamber (not shown). One surface of boss 14 constitutespart of an injector face 16 formed with an annular bevel groove 17. Asidewall portion 19 of boss 14 is formed with an annular groove 18 whosefunction is described below. Formed in the center of main body 12 is aninlet 20 through which propellant, such as oxidizer, is supplied. Aplurality of ports 22 are formed in the bottom wall defining inlet 20.Extending between ports 22 and bevel groove 17 are a series of divergentdrill holes, such as 24 and 26, through which oxidizer is supplied tothe combustion chamber.

Positioned in tight-sealing relationship on boss 14 is a manifold ring40 having an inner wall 42 and an outer wall 44. Formed on inner wall 42is a bevel-shaped annular groove 46 facing annular groove 18 whichgrooves together define a manifold chamber 47. Main body 12 isfabricated with a fuel inlet 30 that is in communication with chamber47. Extending between chamber 47 and bevel groove 17 is a series ofconvergent drilled holes such as 25 and 27. In a similar manner,extending between chamber 47 and outer wall 44 of ring 40 is a series ofdivergent drill holes such as 48 and 49. Fuel supplied through inlet 30is conducted through manifold chamber 47 and is then expelled throughopenings 25, 27, 48 and 49 into the combustion chamber.

Injector assembly 10 is designed to service a bipropellant system,although injectors machined to service monopropellant systems could alsobe made in accordance with the instant invention. The series of holesrepresented by holes 48 and 49 are boundary layer coolant orificesthrough which fuel is sprayed, for cooling purposes, onto the interiorsurface of the combustion chamber. This cooling result could be achievedwithout any holes in manifold ring 40 by various other cooling systemssuch as one of the many well-known regenerative cooling arrangements.The streams of propellant issuing from the adjacent holes 26 and 27,which together constitute a doublet, impinge with one another and becomeatomized and mixed. Together with similar impinging propellant streams,a predetermined resultant spray fan is developed which is fed into thecombustion chamber.

Referring to FIG. 2, main body 12 is formed with an annular recess 50for receiving one end of manifold ring 40 as shown in FIG. 1. Sidewall19 includes an outer sealing surface 32 and an inner sealing surface 34.If recess 50 were not present, then in order to provide the necessarypredetermined sealing surface, boss 14 would project further into thecombustion chamber with the adverse result that additional space wouldbe occupied and there would be a weight increase. Recess 50 can be ofsufficient depth so that boss 14 rather than being raised from injectorface 16 is flush with it.

Mounted in main body 12 and offset from boss 14 is a locat ing pin 55which is used to properly index injector assembly 10 to the combustionchamber. Port 57 is used for sensing the combustion chamber pressure.The outer periphery of main body 12 constituting a flange 52 may besecured by any suitable means such as welding or bolting to thecombustion chamber.

Before manifold ring 40 and main body 12 are assembled as a unit toconstitute injector assembly 10, each is fabricated by machining.Drilling the various propellant supply holes can be postponed untilafter manifold ring 40 and main body 12 are assembled. The componentscan be fabricated from 321 Cres stainless steel, 6061 T-6 aluminumalloy, or any other standard metal suitable for making injectors. When321 Cres stainless steel is used in fabricating both ring 40 and mainbody 12 and injector 10 is to be used for developing I00 pounds thrust,then the diameter of boss 14 will be approximately 1 inch. The thrustingunit could be for attitude control fore assembly, the outer diameter ofboss 14 exceeds the inner diameter of ring 40 by a distance in the orderof 0.002 to 0.004 inches. Ring 40 is then heated to between 900 and1,000 F. in which temperature range the inner diameter of ring 40 willbe enlarged sufficiently to exceed the outer diameter of boss 14.Preferably, the heating is achieved by an induction heating procedure inwhich an electrical coil is wrapped around the ring and is removed whenthe desired temperature is attained.

Ring 40 is then accurately positioned on boss 14 making an interferencefit with it in the order of from 0.002 to 0.004 inches, main body 12being maintained at room temperature or at least at a temperature muchcooler than that of ring $0. With the components held in the desiredrelationship, ring 40 is shrunk, preferably by cooling with a suitablegas such as air. A tight shrink fit is then achieved between boss 14 andring 40. At this point injector assembly has been self-sealed and allpotential leakage paths have been blocked.

The sealing surface constituted by surfaces 32 and 34 of sidewall 19 andinner wall 42 of ring 40 become tightly clamped together sufficient towithstand anticipated pressures. Under these conditions the sealingsurfaces are held together with 15,000 p.s.i. and the normal pressure ofthe fluid to be injected is 300 p.s.i.

Although the sealing pressure for injector i0 is designed with a highsafety factor, it is well known that unexpected high-pressure surges arelikely to occur in injectors and like constructions. The force generatedby a pressure surge is often adequate to blow off a plug or othercomponent such as a ring, like manifold ring 40. In conventionalinjectors when a ring is blown off there is an accompanying pennanentdestruction of the high-strength connecting elements or permanentrupturing of a brazed or welded joint. When this occurs, propellant willflow through the resulting leakage paths causing at least greatcombustion instability and very possibly even more disasterousconsequences. Once the leak. path is developed, it cannot be closed andthe potentially dangerous situation cannot therefore be repaired.

According to the instant invention, injector 10, under somecircumstances, is self-correcting; i.e., it is capable of curingpotential dangers posed by developing leakage passages. For example,when a great pressure surge separates part of ring 40 from boss 14,propellant will flow through the resulting clearances causing combustioninstability. However, as long as the elastic limit of the material fromwhich ring 40 is constructed is not exceeded then ring 40 will notexperience permanent deformation. After the surging condition haselapsed, ring 40, due to the elastic memory of the material, willcontract to its original position and once again become tightly seatedon boss 14. Thus, the original sealing pressure will be restored andnormal flow from injector it) will continue. It should be notedtherefore that leakage passages developed due to excessive pressuresurges, as long as the burst pressure or elastic limit pressure is notattained will only create temporary irregular flow.

Another advantageous feature of the instant invention is that injector10 is internally manifolded; i.e., the manifolding faces the combustionchamber so that if the burst pressure of injector 10 is exceeded, alldamage is confined to the combustion chamber. The leakage passages wouldall be formed on the injector face lid side of injector so that theuncontrolled and erratic propellant discharge would be fed into thecombustion chamber. Therefore, if failure is to occur at all it is atleast confined to disrupting combustion in or destroying the combustionchamber. in contrast, due to burdensome machining problems, mostconventional injectors are externally manifolded; i.e., manifolded onthe back face of the injector (the side not facing the combustionchamber) so that propellant can spray into the space vehicle itself orthe like causing more expensive damage and perhaps complete destruction.Due to the fact that injector 110 is internally manifolded there is nopotential leak passage to locations outside of the combustion chamberConventional in ectors require a great deal of time for inspectionprocedures and quality control certification. injector 10 can be quicklyand accurately certified first by a dimensional inspection to assurethat the correct space differential between boss l4 and ring 40 exists,and secondly, by a standard hydrostatic test to assure that ring 40 isadequately sealed and that ring 40 will withstand the design pressures.Much time is saved during inspection and certification because injector10 has no connectors or welded or brazed joints.

The foregoing specific embodiments and descriptions of the instantinvention are intended only to illustrate and not narrow the underlyinginvention, the scope and spirit of the invention being expressed in thefollowing claims.

lclaim:

l. A process of making a fluid injector having a main body with acircular-shaped boss portion and a ring whose inner diameter, when thering and main body are separated and at the same temperature, is smallerthan the outer diameter of the circular-shaped boss portion, comprisingthe steps of;

providing a peripheral circular manifold groove inter mediate theextremities of the boss portion, thermally altering at least one of themain body and ring until the ring inner diameter becomes larger than theouter diameter of the circular-shaped boss portion,

placing the ring onto the circular-shaped boss portion,

bridging both sides of the groove with said ring, and

thermally altering at least one of the main body and ring until the ringand portions of said boss portion adjacent both edges of said groovesimultaneously become tightly sealed together, whereby said manifoldgroove has an absence ofleakage paths.

2. The process of claim 1, wherein the first thermally altering step ischaracterized by heating the ring, causing it to expand until its innerdiameter becomes larger than the outer diameter of the circular-shapedboss portion, and

the second thermally altering step is characterized by shrinking thering, causing it and the portions of the circular-shaped boss portion tobecome tightly sealed together.

1. A process of making a fluid injector having a main body with a circular-shaped boss portion and a ring whose inner diameter, when the ring and main body are separated and at the same temperature, is smaller than the outer diameter of the circularshaped boss portion, comprising the steps of; providing a peripheral circular manifold groove intermediate the extremities of the boss portion, thermally altering at least one of the main body and ring until the ring inner diameter becomes larger than the outer diameter of the circular-shaped boss portion, placing the ring onto the circular-shaped boss portion, bridging both sides of the groove with said ring, and thermally altering at least one of the main body and ring until the ring and portions of said boss portion adjacent both edges of said groove simultaneously become tightly sealed together, whereby said manifold groove has an absence of leakage paths.
 2. The process of claim 1, wherein the first thermally altering step is characterized by heating the ring, causing it to expand until its inner diameter becomes larger than the outer diameter of the circular-shaped boss portion, and the second thermally altering step is characterized by shrinking the ring, causing it and the portions of the circular-shaped boss portion to become tightly sealed together. 